Ancient Seaways Carried Alligators to South America

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Crocodilian fossil skulls found in the Panama Canal may provide
the missing link between the mouthy reptiles of North America and
their kin in South America, scientists say.

The skulls belong to two new species of ancient crocodilians (a
group that today contains alligators, crocodiles, caimans and
gharials) that lived about 20 million years ago during the
Miocene epoch. These new findings, detailed in the March issue of
the Journal of Vertebrate Paleontology, suggest these alligator
brethren slinked between the continents using ancient seaways
much earlier than once thought.

"The tropics hold some of the greatest diversity on the planet.
Yet there's still so little that we know about them," study
co-author Jonathan Bloch, a paleontologist at the Florida Museum
of Natural History, told LiveScience. The fossil record in
Central America is limited, because rocks there tend to be
covered by forest, Bloch said, so the
Panama excavation provides "a new window back into the past
that's very difficult to get at in the tropics."

An interdisciplinary team found the fossils of the new species,
Culebrasuchus mesoamericanus and Centenariosuchus
gilmorei, during the current expansion of the Panama Canal,
as part of a fossil hunt called the Panama Canal
Project. Culebrasuchus mesoamericanus was probably
about 6- to 7-feet-long and Centenariosuchus gilmorei
was about 4- to 5.5-feet long, the researchers say. Analysis of
the reptiles' evolutionary trees revealed the new species are
related to caimans, South American relatives of
alligators. [ See
Photos of Monster Reptiles ]

When these creatures lived, North America and South America were
separated by a seaway. It was only later, some 2.6 million years
ago, the Isthmus of Panama rose up to form a land bridge between
the continents. That pathway allowed mammals such as armadillos
and
giant sloths to move into North America while relatives of
horses and other animals spread into South America.

The discovery that the new crocodilian species was related to
caimans found in South America before the emergence of the land
bridge suggests the caimans' ancestors crossed a saltwater seaway
to reach South America. The finding is somewhat surprising,
because alligator and crocodile species lack salt glands for
processing seawater. Recent evidence suggests that perhaps the
seaway separating not as wide as scientists thought, the authors
say.

These caiman predecessors probably followed a North-to-South
migration, lead author Alex Hastings, a paleontologist at Georgia
Southern University, told LiveScience. "We know there was a
transition from alligators to caimans, but we didn't have any
evidence [until now]," Hastings said. "We are just scratching the
surface of what we can learn from Central America."